This invention generally relates to mass spectrometers and, more particularly, to filament holder assemblies for use in mass spectrometers.
Mass spectrometers are used in the qualitative analysis of various materials. Typically, a sample to be analyzed is formed on a filament of a high work function material such as platinum (Pt) or rhenium (Re) and the filament is heated for ion emission from the sample material. The emitted ions are then focused in an electrostatic lens assembly and accelerated into an electromagnetic field for ion separation and collection. It will be appreciated that ion emission, acceleration. and separation occur in a vacuum. It will also be appreciated that the emission of ions from impurity elements which are not part of the sample can greatly alter the results.
In conventional mass spectrometers, specimens are formed by attaching a filament across pins which are electrically connectable for heating the filament and which are insulatingly attached within the mass spectrometer. Specimen assemblies are inserted within the mass spectrometer one at a time to undergo a period of specimen preparation by preheating the specimen on the filament to get rid of impurities and to off-gas the specimen before analysis. The actual specimen analysis time may be quite short, but substantial time is required to first establish a vacuum and then to properly preheat the specimen filament before the analysis step.
In one attempt to provide an apparatus for measuring a number of samples in sequence, a rotatable filament holder is produced by Varian MAT as MAT 261, an automatic thermal ionization isotope mass spectrometer. The rotating turret provides electrical contacts using wiper-type contacts against wire leads. This arrangement does not provide reliable and consistent contact resistance, and heating current variations arise with resulting variations in the ion beam and concomitant measurement inaccuracies. Further, the Varian device is assembled from numerous pieces fabricated from sheet stock. A low thermal mass is obtained which allows undesirable thermal transients to occur. Further, a large surface area is produced which requires substantial time to precondition in a vacuum to prevent sample contamination from surface impurities and absorbed gases.
The present invention provides for multiple sequential sample analysis in a rotating turret having a high degree of reproducible conditions and thermal stability for sample analysis and further provides reusable filament holders to improve operator convenience and to reduce costs.
Accordingly, one objective of the present invention is to provide an apparatus for sequential analysis of multiple filamentary samples which are loaded in a common vaccuum system.
Another objective of the present invention is to provide an apparatus which enables a sample to be pretreated for analysis in parallel with a sample analysis, but without contaminating the analysis results.
One other objective of the present invention is to provide stable, rotatable electrical contacts for consistent, reproducible current delivery for filament heating.
A further objective of the present invention is to provide a sequential analysis system having few parts yet with a large heat capacity for thermal stability.
Still another objective of the present invention is to provide improved cleanability and decontamination for rotating components, particularly insulative parts.
Yet another objective of the present invention is to provide a reusable filament pin holder.
One more objective of the present invention is to provide component material having surface characteristics and a minimum surface area effective for reduced surface contamination.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.